JPH0735586B2 - Colored ferritic stainless steel and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a colored ferritic stainless steel and a method for producing the same, and more specifically, a building material and a decorative article (for example, an aesthetic effect or the like) that requires a design property such as an aesthetic effect. , Roofs, interior and exterior of buildings, doors around entrances, sashes, building hardware, etc., automotive exterior materials (malls, wipers, mufflers, etc.), kitchen equipment materials (sinks, bathtubs, etc.), home appliances, electronics and OA The present invention relates to a colored ferritic stainless steel most suitable for devices and the like and a method for producing the same.

(Prior Art) As a coloring method for stainless steel, there are a wet oxidation coloring method, an organic / inorganic coating method, an ion plating method, and the like. Among them, a sulfuric acid / chromic acid mixed aqueous solution which is one of the wet oxidation coloring methods is used. Since the oxide film coloring method for coloring was developed, clear and uniform coloring has become possible, and colored stainless steel sheets have come to be used for building materials and the like.

However, in the case of the oxide film coloring method, an amorphous and transparent oxide film of about 0.1 to 0.5 μm is formed on the steel plate surface,
The color tone is due to the interference of light in the film and the film thickness,
It changes slightly depending on the surface condition of the substrate (mirror surface, BA, HL, etc.). The stainless steel applied to such an oxide film coloring method is austenitic stainless steel typified by SUS304 steel, and is not currently applied to inexpensive ferritic stainless steel typified by SUS430 steel. It was

The reason is that when immersed in a mixed solution of sulfuric acid and chromic acid, SUS430 steel adheres to the magnet and is difficult to distinguish from ordinary steel. Was also one of the major factors.

This streak is caused by a large number of stripes with a width of 2 to 5 mm appearing on the surface of the steel plate, as shown schematically in FIG. 1, and when it occurs, the color becomes dull and uniform. Coloring becomes difficult.

By the way, some proposals have been made so far regarding the uniform coloring technology for ferritic stainless steels, and the typical prior arts and their problems are shown below.

(1) Japanese Patent Application Laid-Open No. 51-120939: This invention relates to a technique for producing a vivid color, which uses sulfuric acid-
During the coloring treatment with the chromic acid mixed aqueous solution, as a pretreatment, `` immersing or electrolyzing SUS430 steel in a mixed aqueous solution containing an acid such as sulfuric acid and nitric acid, an oxidizing agent such as chromic anhydride, and a metal salt such as iron, nickel, and manganese. It is a method of performing "processing". However, because of the pretreatment, there is a problem of cost increase even if inexpensive SUS430 steel is used.

(2) Japanese Patent Application Laid-Open No. 61-23746: This invention is intended to provide a clear colored ferritic stainless steel by trying to improve the composition.
Of the structure of conventional ferritic stainless steel, the content of Cr was slightly increased (Cr 18.0 to 20.0%), and
Furthermore, since Cu (0.3 to 1.0%) and Nb (0.2 to 1.0%) are contained, there is a problem of cost increase in composition.

(3) JP-A-63-235482: This invention is a method of immersing a ferritic stainless steel containing 0.50 to 2.0% Si in an aqueous solution of sulfuric acid and copper sulfate. However, increasing the base material Si to 0.5% or more is
However, it is not suitable as a general steel because it solid-solution strengthens the matrix, increases the yield strength, and lowers the elongation, and there is also the problem of cost increase due to Si.

(Problems to be Solved by the Invention) As described above, although some proposals have been made for the coloring method of ferritic stainless steel even in the related art, the methods (1) to (3) described above are used. Even if it was used, the color was not sufficiently improved, and the uneven streaks did not disappear in particular, and the problem of the decrease in the color due to uneven streaks remained.

Also in terms of cost, (1) pretreatment cost, (2),
In the case of (3), the compositional cost increases greatly, and it is not satisfactory as an inexpensive ferritic colored steel.

Thus, an object of the present invention is to provide an inexpensive colored ferritic stainless steel typified by SUS430 steel in which no streak is observed even when colored by an oxide film coloring method, and a method for producing the same.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present inventor has studied various methods for obtaining a homogeneous colored film by an oxide film coloring method without inviting an increase in manufacturing cost. Especially, the cause and mechanism of occurrence of streak were considered as follows.

(1) "Streaky spots" generated when the oxide film of ferritic stainless steel is colored are parallel to the rolling (stretching) direction of the material.

(2) Therefore, "straightening" is a cause similar to "ridging", hot-rolled colony (region with similar crystal orientation)
Was further attributed to the crystal orientation unevenness caused by the cold rolling.

(3) There are many unclear points about the mechanism of coloring by the oxide film formation process, that is, the mechanism of formation of the interference film, but the elution rate of Fe ion and Cr ion of the material differs depending on the crystal orientation of the material, and it is generated. It was also presumed that the thickness of the interference film was affected, and eventually the difference in crystal orientation of the surface layer crystal grains of the material resulted in a color tone difference, resulting in "straightening".

Based on such an idea, the present inventor has found that as a material, the crystallographic orientation of the surface layer portion (about 10 μm) is random.
It was concluded that "streaky streaks" could be eliminated by using 430 steel, that is, by using at least the surface layer portion of 430 steel having a random texture, and then, through many experiments, it was confirmed and the present invention was completed.

Here, the gist of the present invention is at least (22
2), (211), (110), (200) plane texture X-ray integrated intensity ratio of the texture does not exceed 3.0, characterized by forming a colored film on the surface of ferritic stainless steel It is a colored ferritic stainless steel.

From another aspect, the present invention provides at least (222),
On the surface of ferritic stainless steel where the X-ray integrated intensity ratio of any of the (211), (110) and (200) faces does not exceed 3.0,
A method for producing a colored ferritic stainless steel, which comprises coloring by contacting an aqueous solution containing chromic acid and sulfuric acid.

That is, according to the present invention, the above-mentioned random texture is defined as "at least (222), (211), (110), (200) plane texture X-ray integrated intensity ratio does not exceed 3.0". That is why it is specified.

(Operation) Next, the configuration of the present invention and the effects obtained thereby will be described in detail.

The present invention has a random texture at least the surface layer in order to prevent uneven streaks that occur during coloring by a conventional oxide film coloring method, and a mixed aqueous solution of sulfuric acid and chromic acid is applied to the steel surface thus prepared. The oxide film is formed by bringing them into contact with each other.

Therefore, a method for producing a ferritic stainless steel having such a random texture in at least its surface layer will be described.

As a method of obtaining SUS430 steel having a random texture targeted by the present invention, the following typical methods can be mentioned.

(I) Hot rolling a ferritic stainless steel slab at 850 ° C or higher, quenching immediately after the rolling at a cooling rate of 10 ° C / S or higher, and winding it at a temperature of 550 ° C or lower to form ferrite and martensite. A method of forming a two-phase structure, then performing cold rolling with a cumulative reduction of 50% or more, and then annealing.

(Ii) After ferritic stainless steel slab is subjected to normal hot rolling to form a hot rolled coil, it is heated to 850 to 1100 ° C for 0.1 second to
After heating for 10 minutes, quenching at a cooling rate of 10 ° C / S or more.

Among these methods, the method (i) for changing the coiling temperature after hot rolling is first disclosed in Japanese Patent Publication No. 1-1111816 as a roping countermeasure for SUS430 steel. . That is, the method has a coiling temperature after hot rolling of 800 to 600 ° C., which is a low temperature coiled hot rolled sheet of 500 ° C. or less, and cold rolling (plate thickness 3.5 → 0.8 mm) and This is a method in which recrystallization is promoted by performing recrystallization annealing (830 ° C. × 1 minute → AC) and improvement of roping is achieved. In this case, the hot rolling uses a slab with a thickness of 40 mm, heats it up to 1200 ° C, and then hot-rolls it with 7 passes to a plate thickness of 40 → 3.5 mm, finishes it at 900 ° C, and then finishes at 30 ° C / S. After cooling in, it is wound at a predetermined temperature.

However, in the case of the above-mentioned prior invention, the random texture is not clarified, and there is no indication of the effect of such texture on the oxide film coloring.

Typical (222), (211), (110) of the crystal orientation of the surface layer portion after cold rolling and recrystallization annealing of the steel sheet to be treated by the present invention obtained by the method (i) above, (200)
The surface was measured by the X-ray integrated intensity and displayed as a ratio with the intensity in the random orientation, and shown in FIG. This is a JIS SUS430 steel hot rolled material finished at 900 ℃, rapidly cooled at 30 ℃ / S, wound at 450 ℃, then cold rolled to a plate thickness of 3.5 → 0.8 mm, 830 ℃
× 1min → AC annealed. In addition, the results obtained by winding at 800 ° C. and performing bell annealing at 830 ° C. for 160 hours after completion of cold rolling are also shown.

As can be seen from the results in Fig. 2, after winding at 800 ℃, 8
The bell-annealed at 30 ° C x 16hr and the coiled at a high temperature of 800 to 600 ° C have an X-ray integrated intensity of 3 on the (222) plane.
The above shows a strong selective texture. On the other hand, the target steel of the present invention is wound at 550 ° C. or lower, which is a manufacturing condition, and cold-rolled (thickness: 3.5 t → 0.8 mm) and recrystallized (8 mm) without annealing.
The strength of (222) plane is 2.5 in the case of 30 ℃ x 1 minute → AC)
Significantly decreased to below, and the next strongest (211) and (200) faces also fell to the same extent or slightly.

This indicates that the steel sheet under the above-mentioned conditions does not grow preferentially only in a specific crystal plane and is randomly recrystallized, that is, it has a random texture.

Then, such a random texture is realized by cold rolling a martensite structure as hot-rolled or a ferrite / martensite two-phase structure having a large hardness difference, and in that case, it is often found near the martensite. It is considered that the introduced strain promotes random recrystallization.

Therefore, in addition to the method of introducing the winding martensite at a low temperature, for example, SUS430 steel is used as in the above method (ii).
Similar effects can be obtained by heating in the α + γ two-phase region at 850 to 1100 ℃ and then rapidly cooling (10 ℃ / S or more).

SU having a random texture produced in this way
After degreasing with acetone using S430 steel, 500 g / l H ₂ SO ₄ , 250
When immersed in an aqueous solution of g / l CrO ₃ at 80 ° C for 12 minutes, "streak" generated in the rolling direction completely disappeared under the conventional conditions, and a homogeneous colored stainless steel plate was obtained.

The means for forming such an oxide film is not particularly limited as long as it is a method for coloring by forming an oxide film, but there is preferably a method of bringing it into contact with a mixed aqueous solution of sulfuric acid-chromic acid as described above. For this, a known method such as addition of other appropriate additives may be appropriately adopted.

If necessary, the preferred processing conditions are as follows.

Solution structure: H ₂ SO ₄ : 500 g / l ± 100 g / l, CrO ₃ : 250 g / l ± 50 g / l Temperature: 80 ° C ± 10 ° C Contact time: 0.5 to 15 minutes Contact operation: Immersion, spray The steel targeted in the invention is, for example, JI.
It may be an S SUS430 type or the like, and Al, Ti, Cu, Nb, Mo, etc. may be appropriately added if necessary.

In other words, it is not particularly limited as long as the above-mentioned random texture is formed in at least the surface layer and the steel is colored by the oxide film coloring method.

Further, the present invention is not limited to a steel plate, and the same effect can be obtained for all SUS430-based steels in any form such as a steel plate, a bar steel, and a thick plate.

(Examples) The present invention will be specifically described with reference to Examples.

A test steel having the composition shown in Table 1 was melted by 50 kg vacuum melting, forged into a slab having a thickness of 40 mm, and then hot rolled.

The hot rolling heating temperature was 1200 ° C, and rolling was performed to a plate thickness of 40 → 3.5 mm (reduction rate 91%). The finishing temperature, the cooling rate until winding, and the winding temperature were changed. The hot-rolled sheet was annealed by performing short-time continuous annealing and bell annealing. Thickness 3.5 →
After 0.8 mm (reduction rate 77%) cold rolling, recrystallization annealing was performed to obtain a product steel sheet.

The surface of the steel sheet was buffed and polished, and after the acetone resin, a coloring treatment was performed under the conditions shown in Table 2 to visually check "straightening".

With conventional austenitic SUS304 steel, "straightening" does not occur even with steel sheets manufactured under normal hot rolling conditions (No. 1). However, the SUS430 steel that does not have a random texture, that is, that does not satisfy the hot rolling conditions (No.2, No.3) or the one that has been subjected to bell annealing after hot rolling (No.2) is " Streaks occur.

Regarding those having a random texture according to the present invention, that is, No. 4 to No. 7 satisfying the hot rolling conditions defined by the above-mentioned methods (i) and (ii), (however, No. 6, No. .7
Does not satisfy the hot rolling conditions, but alternative treatment is performed by subsequent annealing.)

Similar effects were observed in a wide range of Cr-based stainless steels in which Al, Ti, Nb, N, Mo, Cu, Cr, etc. were added to SUS430 steel (No.8 to No.16).

Therefore, even if the manufacturing process is a method other than the above, the X-ray integrated intensity ratio of the cold rolled annealed sheet is (222), (211), (11
If the strength of both (0) and (200) faces does not exceed 3.0,
That is, it was confirmed that "streak" was eliminated in the SUS430 steel having a random texture.

(Advantages of the Invention) Since the present invention is configured as described above, in the ferritic stainless colored steel, "streak" which has been a problem in the past is solved, a uniform color tone is obtained, and a special component element It becomes possible to manufacture inexpensive colored stainless steel that does not require manufacturing equipment, and it is expected to be utilized for building materials, decorations, etc., which is extremely useful in industry.

[Brief description of drawings]

FIG. 1 is an explanatory view of uneven streaks occurring in SUS430 steel at the time of coloring; and FIG. 2 is an explanatory view showing an influence of a winding temperature after hot rolling on a texture of a cold rolled annealed material.

Claims (2)

[Claims] 1. At least (222), (211), (110),
The texture of any of the (200) faces has an X-ray integrated intensity ratio
A colored ferritic stainless steel characterized in that a colored film is formed on the surface of a ferritic stainless steel having a random texture not exceeding 3.0. 2. At least (222), (211), (110),
The texture of any of the (200) faces has an X-ray integrated intensity ratio
A method for producing a colored ferritic stainless steel, which comprises contacting an aqueous solution containing chromic acid and sulfuric acid with a surface of a ferritic stainless steel having a random texture not exceeding 3.0 to color it.